1. Field of the Invention
The present invention pertains to the field of computer systems. More particularly, this invention relates to computer system power management with device specific characterization of power consumption.
2. Background
Computer systems such as portable computer systems, desktop computer systems, and server systems typically include a power supply subsystem. Such a power supply subsystem supplies electrical current to the components and devices of the computer system. For example, portable or notebook computer systems typically include a battery subsystem that supplies direct current (DC) to devices and components. In addition, desktop or server systems typically include a power supply that converts an alternating current (AC) power source into DC for the devices and components of the computer system.
Typically, such power supplies impose limits on the amount of electrical current available to the computer system. For example, a battery subsystem for a typical prior notebook computer usually provides a limited level of peak electrical current for a limited duration before battery replacement or recharging is required. In addition, the AC power supply in prior desktop or server systems typically imposes an upper limit on the amount of peak electrical current available to the computer system.
Such limits on the availability of electrical current typically imposes a variety of constraints on the operations of computer systems. For example, a desktop or server system having multiple rotating media mass storage devices such as disk drives may exceed the capacity of the power supply under some conditions. Such disk drives usually draw maximum electrical current during startup while the disk platter spins up to the appropriate angular speed. The peak electrical current draw in such a system may exceed the capacity of the AC power supply if multiple disk drives startup concurrently. Such strains on an AC power supply typically causes the power supply voltage level to drop below normal operating levels. Such low voltage levels may cause hardware errors and erroneous system resets. Similarly, excess electrical current draws on the battery supply in a notebook computer system may cause lowered voltage levels and lead to hardware errors and erroneous system resets.
Some prior desktop or server systems implement an over-designed power supply capable of supplying the peak electrical current required to spin up multiple diskdrives concurrently even though normal system operation does not require such peak current levels. Unfortunately, such high capacity power supplies typically increase the cost of such desktop or server systems. In addition, such high capacity power supplies are typically less efficient over a wide range of electrical supply current in comparison to lower capacity power supplies.
Other prior computer systems implement power management mechanisms that attempt to control the amount of electrical current drawn from the power supply. For example, a prior desktop or server system may provide a controlled startup sequence for the disk drives that prevents the system from exceeding the maximum electrical current capability of the AC power supply. In addition, prior power management mechanisms for notebook computers typically switch off the display screen backlight during a startup phase of a disk drive or during some other activity that requires a large electrical current draw from the battery power supply.
Such prior power management schemes usually rely on hard coded values for the electrical current requirements of the computer system. Such hard coded characterizations of power consumption are typically based upon average current consumption measurements obtained during manufacture. Unfortunately, such hard coded values typically provide inaccurate characterizations because the actual electrical current draw of any given device or combination of devices usually varies from such average values. Such inaccurate device power characterizations can lead to excessive current draws on a power supply, and thereby create the low-voltage levels that cause hardware errors and erroneous system resets.
In addition, prior power management mechanisms for notebook computers typically rely on hard coded values for the electrical current requirements of the system. Unfortunately, such hard coded characterizations of power consumption may cause such a system to switch off the display screen backlight during disk drive startup even though the actual disk drive installed in the notebook consumes less electrical current during spin up than the originally specified the disk drive for the system. Unnecessary power management actions such as switching off the screen display backlight creates unnecessary annoyances for the computer user and unnecessary interruptions in other system functions.